Alteration of blood-brain barrier in human brain tumors: comparison of [18F]fluorodeoxyglucose, [11C]methionine and rubidium-82 using PET.

The influence of the blood-brain barrier (BBB) on tracer uptake was investigated in 21 patients with gliomas and meningiomas using PET, [18F]fluorodeoxyglucose (FDG), [18C]methionine (MET) and the K+ analog rubidium-82 (RUB) whose uptake into brain is largely prevented if the BBB is intact. Tracer uptake was quantitated by (1) multiple time graphical plotting providing tracer distribution volume (VD), unidirectional tracer uptake (Ki), and (2) normalized uptake (NU) which is a measure of net tissue radioactivity related to administered activity and body weight. VD, Ki and NU of MET were higher in meningiomas compared to gliomas and were significantly correlated with NU RUB (Spearman rank: p < 0.005 (VD), p < 0.05 (Ki), p < 0.001 (NU)). NU MET correlated with VD (p < 0.001) and Ki (p < 0.005) of MET. For FDG, tumor VD was in the range of contralateral cortex. Ki and NU values of FDG were highest in glioblastomas. NU of FDG correlated significantly with Ki of FDG (p < 0.005) but not with VD. The results suggest, that alteration of MET uptake in tumors is governed by changes of tracer influx across the BBB, whereas FDG uptake is related to tracer metabolism. This makes FDG the appropriate tracer particularly for the differential diagnosis of contrast enhancing lesions in operated and irradiated patients.